Understanding how neuron subtypes are generated from a proliferative zone in the developing brain is a primary goal in the field of developmental neurobiology. A germinal zone in the dorsal hindbrain, the rhombic lip, gives rise sequentially to six topographically separate and ventrally-located nuclei, collectively termed the precerebellar system. We hypothesize that the transcriptional profile in the rhombic lip changes over time, and that these changes underlie, at least in part, this sequential specification and allocation of precerebellar subtypes. To test this, we are generating statistical representations of the rhombic lip transcriptome (genome-wide) at sequential time points, as well as transcriptomes of mature precerebellar nuclei. By analyzing this set of transcriptomes for mRNAs that correlate with the emergence of specific cell types, we have identified candidate specification/sorting genes that now require validation. In Aim 1, we will validate by in situ mRNA hybridization approximately 500 candidate genes. In Aim 2, we will establish a set of markers that break the rhombic lip and the mature precerebellar nuclei into molecularly distinct subpopulations. In Aim 3, we will analyze a handful of the most promising candidates for their functional role in cell fate determination. Remarkably, precerebellar development has been understudied yet has been associated with SIDS and many other CNS disorders.